The present invention relates to dispensing volatile materials such as insecticides, insect repellants, fragrances, and deodorizers. It provides mats designed to be placed on a heater to release the volatile material when the mat is heated.
It is known to impregnate or coat a solid porous mat, including a plastic mat, with a volatile material, and/or to place a volatile material in a metal pan-like structure. These structures are then placed on heaters to cause the volatile to vaporize into the ambient air. See generally U.S. Pat. No. 6,031,967 and WO 99/66791. The disclosure of these publications, and of all other publications referred to herein, are incorporated by reference as if fully set forth herein.
However, there can be a time lag between the initiation of the heating of the mat and when the concentration of active in the room reaches a desired level. For example, when the mat contains an insecticide, it may take a few minutes before the desired level of protection from mosquitoes or other insects is achieved. This is a particular problem where the product is primarily designed to provide a prolonged release of active (e.g. to provide overnight protection against mosquitoes).
To minimize the time lag, one could try increasing the concentration of active in the mat. However, actives are often costly, and in any event the increased concentration may lead to unnecessarily high levels of insecticide or other active being dispensed into the air after the initial period.
Another approach would be to modify heaters so that they work at one temperature during an initial phase and then work at a reduced temperature at all other times. However, much of the public is unlikely to want to throw away their existing heaters and pay the cost of new ones having this capability. In any event, including this capability in future heaters would unnecessarily increase the cost of such heaters.
U.S. Pat. No. 5,657,574 proposed a mosquito coil having a uniform concentration of insect control agent spread throughout it, but with the coil having an enlarged ignition end. When the coil was first lit an extra burst of insecticide was dispensed because more of the coil was burnt at that time. However, this approach is not suitable for a mat where the entire bottom of the mat is designed to be exposed to the heat source at once.
WO 99/66791 provided a slab-type mat for insertion in an indexed fashion into a heater. Discrete regions of the mat are heated in sequence. The primary purpose of the slab is to provide a mechanism for indexing a new mat section over the heater when the preceding section had been used up. However, the publication also describes that the sequential regions could carry different volatile ingredients or different concentrations of the same volatile ingredient. One example that is given is providing a high concentration section to be used at night and a low concentration section to be used during the day. Unfortunately, this approach requires the user to sequentially move the slab when the next stage of usage is desired.
U.S. Pat. No. 6,551,560 disclosed a mat comprising an outer mat and a central lower section separated by a vertical groove extending through the mat. Different insecticides, or different concentrations of actives, could be provided in each of the two cellulosic sections. The central section was typically heated more quickly (as low cost heaters, such as those typically used in developing countries, often heat the hottest near the center of the heater). As a result, the insecticide in the central portion was dispersed more quickly, while that in the outer mat was dispersed more slowly.
These mats were somewhat difficult to manufacture because the material had to be cut entirely through, resulting in multiple pieces needing to be assembled. This added to the cost of production.
U.S. Pat. No. 4,439,415 described a substrate for dispensing insecticidal vapors having distinct regions impregnated with different insecticides or other volatiles. The distinct regions were provided either on a single substrate with the sections separated by a substance for rendering the material non-absorptive, or were constructed from different pieces of substrate which were coupled together. The device again required multiple parts.
GB 2,122,903 taught a substrate having an aluminum foil bottom layer on which one or more paper segments were mounted. The segments were divided by separators, which were constructed of rubber or synthetic resins which prevented permeation of liquid. Therefore, different volatiles could be provided on the segments without having a volatile from a first segment move to a second segment. This method also required difficult manufacturing steps.
Accordingly, a need still exists for improved volatile dispensing mats.